174 



KNOWLEDGE 



[August 1, 1895. 



and the under surface of the lid are covered with nectar- 

 secreting glands. Especially numerous are these on the 

 under surface of the winged petiole. They allure insects 

 to the orifice of the pitcher. The rim is corrugated, and 

 each corrugation corresponds to a bottle-shaped nectar- 

 gland, whose orifice faces the bottom of the pitcher. The 



hair 



l^^gp5i^5P?tite:-fcy 



Fig. 3. — B. Transverse section of leaf -blade of Dionrea mtiscipiila. 

 Notice the jointed sensitive liair and the digestive glands. 



upper part of the inner surface is so very smooth that an 

 insect is unable to obtain a foothold thereon ; the lower 

 part is partly filled with a watery liquid, into which is 

 poured a digestive fluid by peptic glands lining that portion 

 of the inner surface. The upper smooth part has been termed 

 the conducting surface. In the sketch on the following 

 page (Fig. 4, a) is depicted a small portion of it. The 

 lenticular excrescences were considered by the late Prof. 

 Dickson to be modified stomata ; Prof. Macfarlane has 

 lately verified this supposition by finding every transition 

 between these and perfectly formed stomata. What hap- 

 pens is this : one of the stomatic guard cells rises above 

 the level of the epidermis in such, a manner as to cover 

 the other guard cell and the stoma from the view of the 

 observer. The function of these modified stomata is 

 unknown, but it is conjectured that they secrete the greater 

 part of the liquid found in the cavity of the pitcher. In 

 support of this it is to be noted that the pitcher lid is at 

 first closely applied to the rim of the pitcher ; by and by 

 it gradually opens, and never again shuts up. But in 

 unopened pitchers a considerable quantity of liquid is to 

 be found, and Macfarlane states that in species of 

 Nepenthes, with a large conducting area, large quan- 

 tities of liquid are exuded. In any case the liquid, 

 containing an acid and a ferment, acts in a manner quite 

 similar to the digestive action of Drosera, with the 

 result that in the pitcher insects may be found in all 

 stages of decomposition. This decaying mass must act 

 as an attraction to insects in the native haunts of the 

 Nepenthes, causing them to fly straight into the cavity 

 of the pitcher. 



Macfarlane gives an interesting account * of observa- 

 tions made by him on the visits of insects to the Nepenthes 

 in the conservatories of the Eoyal Botanic Gardens, 

 Edinburgh : — " Being in (one of the conservatories) at 8'30 

 p.m. on a clear evening in June, a large cockroach was 

 noticed to be perched on the front part of the corrugated 

 collar of a fine pitcher of N. kJuici/ana. Approaching 

 cautiously, it was seen to bend its head into the pitcher 

 cavity and sweep it rapidly in successive jerks round the 

 inner edge of the corrugated collar, where the products of 

 the marginal glands would lie. Sipping the material from 

 these, it then rested for a moment, and enjoyed with 

 evident relish the cleaning of what adhered to its mandibles. 

 It then repeatedly tried with its fore legs to step on to the 

 conducting surface of the pitcher cavity, but always slipped; 

 so leaving this it reared itself on its long hind legs by 

 planting one on each side of the rim, catching with the 

 middle legs on to the lower sides of the lid. Placing its 

 fore legs on the middle of the lid, it swept with its mouth 

 parts the richly honeyed surface in long lines. But this 

 did not appear to be satisfying, when compared with the 

 product of the marginal glands, for it speedily returned to 

 these and renewed its jerking mode of feeding. It again 

 attempted to get into the pitcher cavity, but finding this 

 unsafe, it finally licked up traces of the marginal gland- 

 secretion which its fore feet had smeared on the corrugated 

 collar. Eunning dowu the outside of the pitcher, it passed 

 up the tendril and on to the under laminar surface, where 

 its presence would have been perfectly unsuspected had 

 any insectivorous birds been in the neighbourhood, and 

 where also, as Mr. Symington Grieve has suggested, it 

 would have been sheltered from the sun's heat in the 

 daytime. I gently scratched the upper surface above where 

 it was, and it at once retraced its steps in a hurried manner, 

 till it reached the outer surface of the pitcher. Here it 

 rested for a time sipping the juice which exuded from 

 alluring glands, but it soon passed to its old position on the 

 collar. Though disturbed a few minutes before, it seemed 

 quite to forget its fright, and again fell to cleaning the 

 marginal gland-orifices with the utmost care and gusto. 

 It rested now and again only to resume operations, once 

 making a short excursion to the lid- surface, which appeared 

 to me to offer far greater attraction, but seemingly 

 regarding this as inferior, it returned to the collar. 

 Constantly trying to get on to the conducting surface, 

 and as often foiled, it again ran up along the tendril to 

 the under surface of the lamina. Again I scratched this, 

 and the former course was taken, the former efforts made. 

 I was greatly struck by the careful way in which, while 

 attempting to pass into the pitcher, it hooked its two 

 strong hind legs over the reflexed collar-margin, and by 

 the ability it showed to pull itself back by these alone, the 

 second as well as the first pair of legs often being inside 

 the pitcher. Tired of its movements after the fifth 

 excursion, and finding that twilight was approaching, I 

 finally jerked it into the cavity with my pencil, as it hung 

 on the ridge exploring the interior. In its fall it quickly 

 spread out its long legs agamst the sides of the conducting 

 surface, and struggled violently to get out. For a short 

 time this proved useless — it rather slipped deeper ; but 

 after one severe effort it hooked the claws of its fore legs 

 over the corrugated i-im, and pulled itself out. I con- 

 sidered that it had fairly earned liberty, and it speedily 

 moved ofi'." 



This observation confirmed the supposition of the great 

 attractive nature of the marginal glands of the corrugated 

 rim. Observations on the visits of ants afforded further 



* " Annals of Botany," Vol. TIL, page 436. 



